Industrial and commercial cooling towers dissipate heat by evaporating a fraction of their circulating water into the atmosphere. Because PFAS compounds are not volatile at normal operating temperatures, they remain in the liquid phase as water evaporates—causing progressive concentration of PFAS in the recirculating water. This evaporative concentration effect, combined with the use of PFAS-containing scale inhibitors, corrosion inhibitors, and biocides in some cooling water treatment formulations, makes cooling towers a significant reservoir and potential discharge point for PFAS in industrial facilities.
The Evaporative Concentration Mechanism
A cooling tower operating at a concentration ratio (cycles of concentration) of 5:1—a typical operating target—will concentrate non-volatile dissolved species, including PFAS, by a factor of five relative to the makeup water. For a facility drawing makeup water at 20 ppt total PFAS from a municipal supply, recirculating water PFAS concentrations will approach 100 ppt before blowdown dilutes the system. Facilities in PFAS-contaminated groundwater regions using on-site wells for cooling makeup water may see substantially higher recirculating water PFAS levels, with potential for worker exposure via drift or aerosol generation.
Beyond concentration of influent PFAS, cooling systems can be an internal source when PFAS-based water treatment chemicals—including fluorinated scale inhibitors and certain biocide formulations—are dosed into the recirculating system. Water treatment chemical suppliers have generally not included PFAS content disclosure in product data sheets, making voluntary PFAS inventories across cooling water chemical programs an important early step in facility PFAS characterization.
Blowdown Management and Treatment Options
Cooling tower blowdown—the periodic or continuous discharge of concentrated recirculating water to control dissolved solids—becomes the primary PFAS discharge pathway from cooling systems. Facilities discharging blowdown to surface waters under NPDES permits or to municipal sewers under pretreatment programs must characterize PFAS in their blowdown when required by permit or pretreatment authority. Depending on the receiving water’s PFAS sensitivity and applicable effluent standards, treatment of blowdown prior to discharge may be required.
Treatment options for cooling tower blowdown PFAS removal parallel those for other industrial wastewaters: GAC adsorption for moderate-volume, lower-concentration streams; single-use IX resin for lower volumes or where short-chain PFAS predominate; and membrane treatment for facilities with significant blowdown volumes that also need to manage total dissolved solids. For facilities that recycle blowdown through on-site water reuse systems, treatment to remove PFAS before return to the cooling loop can prevent progressive accumulation.
Proactive cooling tower PFAS management should include annual PFAS profiling of makeup water, recirculating water, and blowdown; chemical supplier disclosure requirements for PFAS content in water treatment products; and evaluation of fluorine-free alternative chemistries for scale and corrosion control. Several major water treatment chemical companies have introduced PFAS-free cooling water programs that have demonstrated comparable performance to fluorinated alternatives in field trials at industrial facilities.